I have found that you can get leg bands of one color or another at the local farm supply stores.. DO NOT BUY THEM ONLINE.. I have noticed that prices on line are out of this world lately...people have gone chicken crazy.. and they are definitely uping the prices lately.. do your research and visit you local farm supply stores...
I'm using the colored zip ties idea. Got a whole can of them at Home Depot for a few bucks in different neon colors. There are several sizes in the can, but I use the smallest (4 " I think). Easy to put on, thin and small enough that they don't bother the chickens (after they get used to them), and easy to clip off and put new ones on as they grow.
I used the zip-ties, too. Worked good for me. Just leave em loose enough for growth, but not so loose as to cause problems. I used different colors for cockerels and pullets as I was able to id gender.